This page of the Baldur's Gate 3 guide includes the walkthrough of Ask the Goblin Priestess for Help quest. This walkthrough will help you complete the quest successfully.
- Follow Priestess Gut;
- drink the priestess's potion.
Once you get into the Goblin Camp, you can easily head to the Shattered Sanctum (M6;9). If you use the power of the parasite, you'll go in there without a fight. Inside, you'll encounter priestess Gut. During the conversation, she offers to remove the parasite. If you agree, she tells you to follow her to another room.
However, she does not agree to perform the ritual when the character is not alone with her. So you have to separate the protagonist from the others, lead the group out of the room, and start the conversation.
If you follow the priestess's instructions, you will be trapped and the worm will still be in your head. You have to pass the skillcheck successfully to get free. It will provoke a fight where you will have to face a large group of opponents. First, kill the priestess, then set the team at the top of the stairs to gain High Ground advantage.